The present invention relates to LADAR and, in particular, it concerns a LADAR system in which illumination pulses are spatially and temporally distributed in order to achieve plural pixel resolution within an area sensed by a single detector.
LADAR systems create 3D image of the an object or terrain by transmitting time varying light to various directions in their Field Of View (FOV) and measuring the time it took the light to reach the detector after being reflected. The result is effectively a surface map of the viewed scene, where each pixel value corresponds to a distance from the LADAR system to the object viewed. This will be referred to herein as a LADAR “image”.
LADARS are designed according to two main architectures:                Staring LADAR is based on a matrix of detectors that stare at the relevant Field Of View (FOV) and the illumination is performed by a pulsed laser that illuminate all the FOV instantaneously. Unfortunately, this method requires high power laser in order to generate the required Signal Noise Ratio (SNR) in every pixel of the detector.        Scanning system is based on partial illumination of the total Field Of Regard (FOR) by a smaller scanned FOV (in most cases a line illumination). Consequently only part of the FOR is illuminated at a time and the power requirement from the laser is reduced. However, at some applications where long range is required the laser can not generate the required power. Furthermore, in order to have a compact design of the LADAR, further reduction of the number of detectors is needed.        
Fiber based lasers are becoming the workhorse of the laser industry because of their low cost of ownership and reliability. Unfortunately, fiber technology is limited in term of output power. Therefore, it is very difficult to implement fiber lasers in LADAR systems.
Receiver technology is also expensive and complicated therefore, methods where developed for utilizing single receiver for interpreting the signal received from various directions by utilizing Time Domain Multiplexing (TDM) technology. In patent US20020020806A1 TDM is achieved at the receiver by using different fiber length as presented in FIG. 1. A very high power laser is transmitting 51 light pulses which are split simultaneously to the relevant FOV by optics 62. The light travels in free space and being reflected as a signal back to the receiver (schematically represented as 64). Multimode fiber tips are located at the focal plane of the receiving optics where each fiber has different length 66. Consequently, the signal arrives to the detector at different times from different sections or directions of the FOV.
Unfortunately, this method requires high power laser in addition to the fact that substantial loss is introduced to the signal by the optics and the fibers. Furthermore, the alignment of the receiving fiber tips to the transmission optics is complicated and unreliable.
There is a need for a technology that will enable the use of reliable fiber lasers in LADAR systems by reducing the need for high intensity output, without compromising on system performance. This technology should be compact in size in order to fit to most portable applications. Furthermore, there is a need for a method to split the laser light to the various sections of the FOV while introducing minimal loss. The required system should be robust to misalignment between the transmitting and receiving optics.